[MSSA] Add an overload for getClobberingMemoryAccess.

A seemingly common use for the walker's getClobberingMemoryAccess
function is:

```
MemoryAccess *getClobber(MemorySSAWalker *W, MemoryUseOrDef *MUD) {
  const Instruction *I = MUD->getMemoryInst();
  return W->getClobberingMemoryAccess(I);
}
```

Which is kind of redundant, since walkers will ultimately query MSSA to
find out which MemoryAccess `I` maps to (...which is always `MUD`).

So, this patch adds an overload of getClobberingMemoryAccess that
accepts MemoryAccesses directly. As a result, the Instruction overload
of getClobberingMemoryAccess becomes a lightweight wrapper around our
new overload.

Additionally, this patch un`virtual`izes the Instruction overload of
getClobberingMemoryAccess, since there doesn't seem to be a walker that
benefits from that being virtual, and I can't think of how else one
would implement it. Happy to make it virtual again if we would benefit
from doing so.

llvm-svn: 276169

1 files changed, 9 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/Utils/MemorySSA.cpp b/llvm/lib/Transforms/Utils/MemorySSA.cpp
index f28057b107f..d7dbc516619 100644
--- a/llvm/lib/Transforms/Utils/MemorySSA.cpp
+++ b/llvm/lib/Transforms/Utils/MemorySSA.cpp
@@ -900,7 +900,8 @@ public:
   CachingWalker(MemorySSA *, AliasAnalysis *, DominatorTree *);
   ~CachingWalker() override;
 
-  MemoryAccess *getClobberingMemoryAccess(const Instruction *) override;
+  using MemorySSAWalker::getClobberingMemoryAccess;
+  MemoryAccess *getClobberingMemoryAccess(MemoryAccess *) override;
   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *,
                                           MemoryLocation &) override;
   void invalidateInfo(MemoryAccess *) override;
@@ -1850,11 +1851,13 @@ MemoryAccess *MemorySSA::CachingWalker::getClobberingMemoryAccess(
 }
 
 MemoryAccess *
-MemorySSA::CachingWalker::getClobberingMemoryAccess(const Instruction *I) {
-  // There should be no way to lookup an instruction and get a phi as the
-  // access, since we only map BB's to PHI's. So, this must be a use or def.
-  auto *StartingAccess = cast<MemoryUseOrDef>(MSSA->getMemoryAccess(I));
+MemorySSA::CachingWalker::getClobberingMemoryAccess(MemoryAccess *MA) {
+  auto *StartingAccess = dyn_cast<MemoryUseOrDef>(MA);
+  // If this is a MemoryPhi, we can't do anything.
+  if (!StartingAccess)
+    return MA;
 
+  const Instruction *I = StartingAccess->getMemoryInst();
   UpwardsMemoryQuery Q(I, StartingAccess);
   // We can't sanely do anything with a fences, they conservatively
   // clobber all memory, and have no locations to get pointers from to
@@ -1888,8 +1891,7 @@ void MemorySSA::CachingWalker::verifyRemoved(MemoryAccess *MA) {
 }
 
 MemoryAccess *
-DoNothingMemorySSAWalker::getClobberingMemoryAccess(const Instruction *I) {
-  MemoryAccess *MA = MSSA->getMemoryAccess(I);
+DoNothingMemorySSAWalker::getClobberingMemoryAccess(MemoryAccess *MA) {
   if (auto *Use = dyn_cast<MemoryUseOrDef>(MA))
     return Use->getDefiningAccess();
   return MA;